White light emitting phosphor blends for LED devices

ABSTRACT

There is provided white light illumination system including a radiation source, a first luminescent material having a peak emission wavelength of about 575 to about 620 nm, a second luminescent material having a peak emission wavelength of about 495 to about 550 nm, which is different from the first luminescent material and a third luminescent material having a peak emission wavelength of about 420 to about 480 nm, which is different from the first and second luminescent materials. The LED may be a UV LED and the luminescent materials may be a blend of three or four phosphors. The first phosphor may be an orange emitting Eu 2+ , Mn 2+  activated strontium pyrophosphate, Sr 2 P 2 O 7 :Eu 2+ , Mn 2+ . The second phosphor may be a blue-green emitting Eu 2+  activated barium silicate, (Ba,Sr,Ca) 2 SiO 4 :Eu 2+ . The third phosphor may be a blue emitting SECA phosphor, (Sr,Ba,Ca) 5 (PO 4 ) 3 Cl:Eu 2+ . Optionally, the fourth phosphor may be a red emitting Mn 4+  activated magnesium fluorogermanate, 3.5MgO*0.5MgF 2 *GeO 2 :Mn 4+ . A human observer perceives the combination of the orange, blue-green, blue and/or red phosphor emissions as white light.

BACKGROUND OF THE INVENTION

[0001] This invention relates generally to a white light illuminationsystem, and specifically to a ceramic phosphor blend for converting UVradiation emitted by a light emitting diode (“LED”) to white light.

[0002] White light emitting LEDs are used as a backlight in liquidcrystal displays and as a replacement for small conventional lamps andfluorescent lamps. As discussed in chapter 10.4 of “The Blue LaserDiode” by S. Nakamura et al., pages 216-221 (Springer 1997),incorporated herein by reference, white light LEDs are fabricated byforming a ceramic phosphor layer on the output surface of a blue lightemitting semiconductor LED. Conventionally, the blue LED is an InGaNsingle quantum well LED and the phosphor is a cerium doped yttriumaluminum garnet (“YAG:Ce”), Y₃Al₅O₁₂:Ce³⁺. The blue light emitted by theLED excites the phosphor, causing it to emit yellow light. The bluelight emitted by the LED is transmitted through the phosphor and ismixed with the yellow light emitted by the phosphor. The viewerperceives the mixture of blue and yellow light as white light.

[0003] However the blue LED—YAG:Ce phosphor white light illuminationsystem suffers from the following disadvantages. The prior art blueLED—YAG:Ce phosphor system produces white light with a high colortemperature ranging from 6000K to 8000K, which is comparable tosunlight, and a typical color rendering index (CRI) of about 70 to 75.In other words, the chromaticity or color coordinates of this system arelocated adjacent to the Black Body Locus (“BBL”) between the colortemperatures of 6000K and 8000K on the CIE chromaticity diagramillustrated in FIG. 1. The color temperature of this system can bereduced by increasing the phosphor thickness. However, the increasedphosphor thickness decreases the system efficiency.

[0004] While the blue LED—YAG:Ce phosphor illumination system with arelatively high color temperature and a relatively low CRI is acceptableto customers in the far east lighting markets, the customers in theNorth American markets generally prefer an illumination system with alower color temperature, while the customers European markets generallyprefer an illumination system with a high CRI. For example, NorthAmerican customers generally prefer systems with color temperaturesbetween 3000K and 4100K, while European customers generally prefersystems with a CRI above 90.

[0005] The chromaticity coordinates and the CIE chromaticity diagramillustrated in FIG. 1 are explained in detail in several text books,such as pages 98-107 of K. H. Butler, “Fluorescent Lamp Phosphors” (ThePennsylvania State University Press 1980) and pages 109-110 of G. Blasseet al., “Luminescent Materials” (Springer-Verlag 1994), bothincorporated herein by reference. The chromaticity coordinates (i.e.,color points) that lie along the BBL obey Planck's equation:E(λ)=Aλ⁻⁵/(e^((B/T))−1), where E is the emission intensity, λ is theemission wavelength, T the color temperature of the black body and A andB are constants. Color coordinates that lie on or near the BBL yieldpleasing white light to a human observer. CRI is a relative measurementof how the color rendition of an illumination system compares to that ofa black body radiator. The CRI equals 100 if the color coordinates of aset of test colors being illuminated by the illumination system are thesame as the coordinates of the same test colors being irradiated by theblack body radiator.

[0006] Another disadvantage of the blue LED—YAG:Ce phosphor system isthat the LED color output (e.g., spectral power distribution and peakemission wavelength) varies with the band gap width of the LED activelayer and with the power applied to the LED. During production, acertain percentage of LEDs are manufactured with active layers whoseactual band gap width is larger or smaller than the desired width. Thus,the color output of such LEDs deviates from the desired parameters.Furthermore, even if the band gap of a particular LED has the desiredwidth, during LED operation the power applied to the LED frequentlydeviates from the desired value. This also causes the LED color outputto deviate from the desired parameters. Since the light emitted by thesystem contains a blue component from the LED, if the color output ofthe LED deviates from the desired parameters, then the light output bythe system deviates form the desired parameters as well. A significantdeviation from the desired parameters may cause the color output of thesystem to appear non-white (i.e., bluish or yellowish).

[0007] Furthermore, the color output of the blue LED—YAG:Ce phosphorsystem varies greatly due to frequent, unavoidable, routine deviationsfrom desired parameters (i.e., manufacturing systematic variations)during the production of the LED lamp because the color output of thissystem is very sensitive to the thickness of the phosphor. If thephosphor is too thin, then more than a desired amount of the blue lightemitted by the LED will penetrate through the phosphor, and the combinedLED—phosphor system light output will appear bluish, because it isdominated by the output of the blue LED. In contrast, if the phosphor istoo thick, then less than a desired amount of the blue LED light willpenetrate through the thick YAG:Ce phosphor layer. The combinedLED-phosphor system will then appear yellowish, because it is dominatedby the yellow output of the YAG:Ce phosphor.

[0008] Therefore, the thickness of the phosphor is a critical variableaffecting the color output of the prior art system. Unfortunately, it isdifficult to control the precise thickness of the phosphor during largescale production of the blue LED—YAG:Ce phosphor system. Variations inphosphor thickness often result in the system output being unsuitablefor white light illumination applications, causing the color output ofthe system to appear non-white (i.e., bluish or yellowish), which leadsto an unacceptably low blue LED—YAG:Ce phosphor system manufacturingyield.

[0009] The blue LED—YAG:Ce phosphor system also suffers from the haloeffect due to the separation of blue and yellow light. The LED emitsblue light in a directional fashion. However, the phosphor emits yellowlight isotropically (i.e., in all directions). Therefore, when the lightoutput by the system is viewed straight on (i.e., directly at the LEDemission), the light appears bluish-white. In contrast, when the lightoutput is viewed at an angle, the light appears yellowish due to thepredominance of the yellow phosphor emission. When the light output bysuch a system is directed onto a flat surface, it appears as a yellowishhalo surrounding a bluish area. The present invention is directed toovercoming or at least reducing the problems set forth above.

BRIEF SUMMARY OF THE INVENTION

[0010] In accordance with one aspect of the present invention, there isprovided a white light illumination system comprising a light emittingdiode, a first luminescent material having a peak emission wavelength ofabout 575 to about 620 nm, a second luminescent material having a peakemission wavelength of about 495 to about 550 nm, which is differentfrom the first luminescent material, and a third luminescent materialhaving a peak emission wavelength of about 420 to about 480 nm, which isdifferent from the first and second luminescent materials.

[0011] In accordance with another aspect of the present invention, thereis provided a white light emitting phosphor blend comprising at leastthree phosphors, wherein the white light emitted by the phosphor blendin response to incident radiation having a peak wavelength between 360and 420 nm comprises a color temperature between 3000K and 6500K, a CRIabove 70 and an efficacy above 200 lm/W.

[0012] In accordance with another aspect of the present invention, thereis provided a white light illumination system, comprising:

[0013] a radiation source;

[0014] a first APO:Eu²⁺, Mn²⁺ phosphor, where A comprises at least oneof Sr, Ca, Ba or Mg;

[0015] a second phosphor selected from at least one of:

[0016] a) an ASiO:Eu²⁺ phosphor, where A comprises at least one of Ba,Ca, Sr or Mg;

[0017] b) an ADSiO:Eu²⁺ phosphor, where A comprises at least one of Ba,Ca or Sr and D comprises at least one of Mg or Zn; or

[0018] c) an AAlO:EU²⁺ phosphor, where A comprises at least one of Ba,Sr or Ca; and

[0019] a third phosphor selected from at least one of:

[0020] d) an AMgAlO:Eu²⁺ phosphor where A comprises at least one of Ba,Ca or Sr;

[0021] e) a DPOCl:Eu²⁺ phosphor where D comprises at least one of Sr,Ba, Ca or Mg;

[0022] f) an EO*AlO:Eu²⁺ phosphor, where E comprises at least one of Ba,Sr or Ca;

[0023] g) an EAlO:Eu²⁺ phosphor, where E comprises at least one of Ba,Sr or Ca; or

[0024] h) GAlO:EU²⁺ phosphor, where G comprises at least one of K, Li,Na or Rb.

[0025] In accordance with another aspect of the present invention, thereis provided a method of making a white light illumination system,comprising blending a first phosphor powder having a peak emissionwavelength of about 575 to about 620 nm, a second phosphor powder havinga peak emission wavelength of about 495 to about 550 nm, and a thirdphosphor powder having a peak emission wavelength of about 420 to about480 nm to form a phosphor powder mixture, and placing the phosphorpowder mixture into the white light illumination system adjacent a lightemitting diode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is an illustration of a CIE chromaticity diagram.

[0027]FIG. 2 is schematic illustration of a white light illuminationsystem according to one embodiment of the present invention.

[0028] FIGS. 3-5 are cross-sectional schematic views of illuminationsystems using an LED according to the first preferred embodiment of thepresent invention.

[0029]FIG. 6 is a cross-sectional schematic view of an illuminationsystem using a fluorescent lamp according to the second preferredembodiment of the present invention.

[0030]FIG. 7 is a cross-sectional schematic view of an illuminationsystem using a plasma display according to the third preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0031] In view of the problems in the prior art, it is desirable toobtain a white light illumination system whose color output is lesssensitive to variations during system operation and manufacturingprocess, such as due to variations in the LED power, the width of theLED active layer band gap and the thickness of the luminescent material.The present inventors have discovered that a color output of theradiation source—luminescent material system is less sensitive to thesevariations if the color output of the system does not includesignificant visible radiation emitted by the radiation source, such asan LED. In this case, the color output of the system does not varysignificantly with the LED power, band gap width and the luminescentmaterial thickness. The term luminescent material preferably comprises aphosphor in loose or packed powder form.

[0032] The color output of the system does not vary significantly withthe thickness of the luminescent material if the white light emitted bythe system lacks any significant visible component emitted by theradiation source, such as the LED. Therefore, the amount of transmissionof the LED radiation through the luminescent material, such as aphosphor, does not affect the color output of the system. This can beachieved in at least two ways.

[0033] One way to avoid affecting the color output of the system is byusing a radiation source that emits radiation in a wavelength that isnot visible to the human eye. For example, an LED may be constructed toemit ultraviolet (UV) radiation having a wavelength of 380 nm or lessthat is not visible to the human eye. Furthermore, the human eye is notvery sensitive to UV radiation having a wavelength between 380 and 400nm and to violet light having a wavelength between 400 and 420 nm.Therefore, the radiation emitted by the LED having a wavelength of 420nm or less would not substantially affect the color output of theled—PHOSPHOR system irrespective of whether the emitted LED radiation istransmitted through the phosphor or not, because radiation having awavelength of about 420 nm or less is not significantly visible to ahuman eye.

[0034] The second way to avoid affecting the color output of the systemis by using a thick luminescent material which does not allow theradiation from the radiation source to pass through it. For example, ifthe LED emits visible light between 420 and 650 nm, then in order toensure that the phosphor thickness does not affect the color output ofthe system, the phosphor should be thick enough to prevent anysignificant amount of visible light emitted by the LED from penetratingthrough the phosphor. However, while this way to avoid affecting thecolor output of the system is possible, it is not preferred because itlowers the output efficiency of the system.

[0035] In both cases described above, the color of the visible lightemitted by the system is solely dependent on the type of luminescentmaterial used. Therefore, in order for the led—PHOSPHOR system to emitwhite light, the phosphor should emit white light when it is irradiatedby the LED radiation.

[0036] Furthermore, by utilizing more than one phosphor the colorproperties of the white light may be varied to meet the desired colorparameters. For example, by selecting certain phosphors in a certainratio, the color temperature and the CRI of the white light or theefficacy of the system may be optimized. For example, phosphor ratiosmay be selected to obtain a white light illumination system with a colortemperature of 3000K to 6500K, a CRI of above 70 and an efficacy ofabove 300 lm/W, which is desirable in the North American markets. Acolor temperature of 4000 to 6500K is particularly desirable for aflashlight. Alternatively, other phosphor ratios may be selected toobtain a white light illumination system with a color temperature of3000K to 4100K, a CRI of above 90 and an efficacy of above 200 lm/W,which is desirable in the European markets.

[0037] The present inventors have discovered that a when a first orangeemitting phosphor having a peak emission wavelength between about 575and 620 nm, a second blue-green emitting phosphor having a peak emissionwavelength between about 495 to about 550 nm, and a third blue emittingphosphor having a peak emission wavelength of about 420 to about 480 areused together, a human observer perceives their combined emission aswhite light. Furthermore, in order to increase the CRI of theillumination system, a fourth red emitting phosphor having a peakemission wavelength of about 620 nm to about 670 nm may be optionallyadded.

[0038]FIG. 2 schematically illustrates the above principle. In FIG. 2, aradiation source 1, such as an LED, emits radiation 2 incident on threeluminescent materials layers 3, such as the above described first,second and third phosphors. The radiation 2 may have a wavelength towhich the human eye is not sensitive, such as 420 nm and below.Alternatively, the phosphors 3 may be too thick to allow significantradiation 2 to penetrate to the other side. After absorbing the incidentradiation 2, the first phosphor emits orange light 4 having a peakemission wavelength between 575 and 620 nm, the second phosphor emitsblue-green light 5 having a peak emission wavelength between 495 and 550nm, and the third phosphor emits blue light 6 having a peak emissionwavelength between 420 and 480. If present, the fourth phosphor emitsred light 7 having a peak emission wavelength between 620 nm and 670 nm.The human observer 8 perceives the combination of the orange 4,blue-green 5, blue 6 and optionally red 7 light as white light 9. FIG. 2schematically illustrates that different color light 4, 5, 6, 7 emanatesfrom discrete phosphor areas to illustrate the concept of color mixing.However, it should be understood that light 4, 5, 6 and 7 may be emittedfrom the same area and/or from the entire phosphor if the individualphosphors are blended together to form a single blended phosphor layer3.

[0039] Any luminescent materials, such as phosphors and scintillatorsmay be used in combination with a radiation source to form the whitelight illumination system. Preferably, the luminescent materials have ahigh quantum efficiency at a particular emission wavelength of theradiation source. Furthermore, each luminescent material is preferablytransparent to the visible light wavelengths emitted by the otherluminescent material.

[0040] 1. The Radiation Source

[0041] The radiation source 1 may comprise any radiation source capableof causing an emission from the phosphors. Preferably, the radiationsource 1 comprises an LED. However, the radiation source 1 may alsocomprise a gas, such as mercury in a fluorescent lamp or high pressuremercury vapor lamp, or a noble gas, such as Ne, Ar and/or Xe in a plasmadisplay.

[0042] For example, the radiation source 1 may comprise any LED whichcauses the phosphors 3 to emit radiation 9 which appears white to thehuman observer 8 when the radiation 2 emitted by the LED is directedonto the phosphors. Thus, the LED may comprise a semiconductor diodebased on any suitable III-V, II-VI or IV-IV semiconductor layers andhaving an emission wavelength of 360 to 420 nm. For example, the LED maycontain at least one semiconductor layer based on GaN, ZnSe or SiCsemiconductors. The LED may also contain one or more quantum wells inthe active region, if desired. Preferably, the LED active region maycomprise a p-n junction comprising GaN, AlGaN and/or InGaN semiconductorlayers. The p-n junction may be separated by a thin undoped InGaN layeror by one or more InGaN quantum wells. The LED may have an emissionwavelength between 360 and 420 nm, preferably between 370 and 405 nm,most preferably between 370 and 390 nm. However, an LED with an emissionwavelength above 420 nm may be used with a thick phosphor, whosethickness prevents the light emitted from the LED from penetratingthrough the phosphor. For example the LED may have the followingwavelengths: 370, 375, 380, 390 or 405 nm.

[0043] The radiation source 1 of the white light illumination system hasbeen described above as a semiconductor light emitting diode. However,the radiation source of the present invention is not limited to asemiconductor light emitting diode. For example, the radiation sourcemay comprise a laser diode or an organic light emitting diode (OLED).The preferred white light illumination system described above contains asingle radiation source 1. However, if desired, plural radiation sourcesmay be used in the system in order to improve the emitted white light orto combine the emitted white light with a light of a different color(s).For example, the white light emitting system may be used in combinationwith red, green and/or blue light emitting diodes in a display device.

[0044] 2. The First Phosphor

[0045] The first luminescent material may be any phosphor, which inresponse to the incident radiation 2 from the radiation source 1, emitsvisible light having a peak emission wavelength of about 575 to about620 nm. If the radiation source 1 comprises an LED having a peakemission wavelength between 360 and 420 nm, then the first phosphor maycomprise any commercially available phosphor having the peak emissionwavelength between 575 and 620 nm and a high relatively efficacy andquantum efficiency for incident radiation having a peak wavelengthbetween 360 and 420 nm.

[0046] Preferably, the first phosphor comprises APO:Eu²⁺, Mn²⁺, where Acomprises at least one of Sr, Ca, Ba or Mg. Most preferably, the firstphosphor comprises a europium and manganese doped alkaline earthpyrophosphate phosphor, A₂P₂O₇:Eu²⁺, Mn²⁺. The phosphor may be writtenas (A_(1-x-y)Eu_(x)Mn_(y))₂ P₂ O₇, where 0<x≦0.2, and 0<y≦0.2.Preferably, A comprises strontium ions. This phosphor is preferred foran LED radiation source because it has a high efficacy and high quantumefficiency for incident radiation having a peak wavelength between 360and 420 nm, such as that emitted by an LED. Alternatively, the firstphosphor may comprise A₃P₂O₈:Eu²⁺, Mn²⁺, where A comprises at least oneof Sr, Ca, Ba or Mg.

[0047] In the Eu²⁺ and Mn²⁺ doped alkaline earth pyrophosphate phosphor,the Eu ions generally act as sensitizers and Mn ions generally act asactivators. Thus, the Eu ions absorb the incident energy (i.e., photons)emitted by the radiation source and transfer the absorbed energy to theMn ions. The Mn ions are promoted to an excited state by the absorbedtransferred energy and emit a broad radiation band having a peakwavelength that varies from about 575 to 595 nm when the A ions compriseSr ions. Alternatively, A may comprise 50 molar percent Sr ions and 50molar percent Mg ions, such that the APO:Eu²⁺, Mn²⁺ phosphor comprises aSrMgP₂O₇:Eu²⁺, Mn²⁺ phosphor which has a peak wavelength of about 615nm.

[0048] 3. The Second Phosphor

[0049] The second luminescent material may be any phosphor, which inresponse to the incident radiation 2 from the radiation source 1, emitsvisible light having a peak emission wavelength of about 495 nm to about550 nm. If the radiation source 1 comprises an LED having a peakemission wavelength between 360 and 420 nm, then the second phosphor maycomprise any commercially available phosphor having the peak emissionwavelength between 495 and 550 nm and a high relatively efficacy andquantum efficiency for incident radiation having a peak wavelengthbetween 360 and 420 nm. For example, the following three Eu²⁺ activatedalkaline earth silicate and alkaline earth aluminate phosphors fit thiscriteria.

[0050] One such phosphor is a divalent europium activated alkaline earthsilicate phosphor, ASiO:Eu²⁺, where A comprises at least one of Ba, Ca,Sr or Mg. Preferably, the ASiO:Eu²⁺ phosphor has the followingcomposition: A₂SiO₄:Eu²⁺, where A preferably comprises at least 60% Ba,30% or less Sr and 10% or less Ca. If A comprises Ba or Ca, then thephosphor peak emission wavelength is about 505 nm. If A comprises Sr,then the phosphor peak emission wavelength is about 580 nm. Therefore, Amost preferably comprises Ba ions or Ba ions with some Ca and/or Sr ionsto obtain a desired peak wavelength.

[0051] In the alkaline earth silicate phosphor, the europium activatorsubstitutes on the alkaline earth lattice site, such that the phosphormay be written as: ((Ba,Sr,Ca)_(1-x)Eu_(x))₂SiO₄, where 0<x≦0.2. Thealkaline earth silicate phosphor may also contain other impurities anddopants. For example, the phosphor may contain a small amount offluorine incorporated during powder processing from a fluorinecontaining flux compound, such as BaF₂ or EuF₃.

[0052] Another divalent europium activated alkaline earth silicatephosphor, ADSiO:Eu²⁺ where A comprises at least one of Ba, Ca or Sr andD comprises at least one of Mg and Zn, is suitable as the secondphosphor. Preferably, the ADSiO:Eu²⁺ phosphor has the followingcomposition: A₂DSi₂O₇:Eu²⁺. The peak emission wavelength and therelative quantum efficiency of each isomorphous phosphor is illustratedin Table I below: TABLE I A D A D A D A D A D A D Sr/ Ca Mg Sr Mg Sr ZnBa Mg Ba Mg Ba Zn Peak λ 535 470 470 440 500 505

[0053] Therefore, A most preferably comprises Ba ions and/or Ba ionswith some Ca or Sr ions in order to obtain the desired peak wavelength.

[0054] In the alkaline earth silicate phosphor, the europium activatorsubstitutes on the alkaline earth lattice site, such that the phosphormay be written as: (A_(1−x)Eu_(x))₂DSi₂O₇, where 0<x≦0.2. The alkalineearth silicate phosphor may also contain other impurities and dopants.For example, the phosphor may contain a small amount of fluorineincorporated during powder processing from a fluorine containing fluxcompound, such as BaF₂ or EuF₃.

[0055] A divalent europium activated alkaline earth aluminate phosphor,AAlO:Eu²⁺, where A comprises at least one of Ba, Sr or Ca is alsosuitable for use as the second phosphor. Preferably, the AAlO:Eu²⁺phosphor has the following composition: AAl₂O₄:Eu²⁺, where A comprisesat least 50% Sr, preferably at least 80% Sr and 20% or less Ba. If Acomprises Ba, then the phosphor peak emission wavelength is about 505nm. If A comprises Sr, then the phosphor peak emission wavelength isabout 520 nm. If A comprises Ca, then the phosphor peak emissionwavelength is about 440 nm. Therefore, A most preferably comprises Sr orSr and Ba ions in order to obtain the desired peak wavelength.

[0056] In the alkaline earth aluminate phosphor, the europium activatorsubstitutes on the alkaline earth lattice site, such that the phosphormay be written as: (A_(1−x)Eu_(x))Al₂O₄, where 0<x≦0.2. The alkalineearth aluminate phosphor may also contain other impurities and dopants,such as fluorine incorporated from a flux.

[0057] The europium activated alkaline earth silicate phosphors aredescribed in detail in G. Blasse et al., “Fluorescence of Eu ²⁺Activated Silicates” 23 Philips Res. Repts. 189-200 (1968), incorporatedherein by reference. The europium activated alkaline earth aluminatesphosphors are described in detail in G. Blasse et al., “Fluorescence ofEu ²⁺ Activated Alkaline-Earth Aluminates” 23 Philips Res. Repts.201-206 (1968), incorporated herein by reference. These references alsoillustrate the emission and excitation spectra of the above describedphosphors.

[0058] In one aspect of the present invention, the second phosphor maycomprise a plurality of the silicate and aluminate phosphors in order tooptimize the color or other emission properties, if desired. Forexample, the second phosphor may comprise the following combinations:ASiO:Eu²⁺ and ADSiO:Eu²⁺, ASiO:Eu²⁺ and AAlO:Eu²⁺, ADSiO:Eu²⁺ andAAlO:Eu²⁺, ASiO:Eu²⁺ and ADSiO:Eu²⁺ and AAlO:Eu²⁺. The above mentionedphosphors may be placed into the same illumination system as overlyinglayers or as a blend.

[0059] 4. The Third Phosphor

[0060] The third luminescent material may be any phosphor, which inresponse to the incident radiation 2 from the radiation source 1, emitsvisible light having a peak emission wavelength of about 420 nm to about480 nm. If the radiation source 1 comprises an LED having a peakemission wavelength between 360 and 420 nm, then the third phosphor maycomprise any commercially available phosphor having the peak emissionwavelength between 420 and 480 nm and a high efficacy and quantumefficiency for incident radiation having a peak wavelength between 360and 420 nm. For example, the following two commercially available Eu²⁺activated phosphors fit this criteria.

[0061] One example of a third phosphor having a peak emission wavelengthbetween 420 and 480 nm is the divalent europium activated halophosphatephosphor, DPOCl:Eu²⁺, where D comprises at least one of Sr, Ba, Ca orMg. The DPOCl:Eu²⁺ phosphor preferably comprises the commerciallyavailable “SECA” phosphor, D₅(PO₄)₃Cl:Eu²⁺. A small amount of phosphatemay be replaced by a small amount of borate to increase the emissionintensity. The peak emission wavelength of this phosphor varies with theratio of strontium to other alkaline earth ions. When D comprises onlySr ions, the peak emission wavelength is 447 nm. Substitution of the Srions with Ba ions cause the peak emission to shift to a lowerwavelength, while substitution of the Sr ions with Ca ions cause thepeak emission to shift to a higher wavelength. For example, if the 0.5moles out of the 5 moles of Sr ions are substituted with 0.5 moles of Caions, then the peak emission shifts to 452 nm. If 1 mole of Sr ions aresubstituted with 0.5 moles of Ca ions and 0.5 moles of Ba ions, then thepeak emission shifts to 445 nm. Therefore, the preferred SECA phosphorcomposition is (Sr_(1-y-z)Ba_(y)Ca_(z))_(5-x)Eu_(x) (PO₄)₃Cl, where0.01≦x≦0.2, 0≦y≦0.1 and 0≦z≦0.1 and the preferred peak emissionwavelength is 447-450 nm.

[0062] Another example of a third phosphor having a peak emissionwavelength between 420 and 480 nm is the divalent europium activatedalkaline earth metal aluminate phosphor, AMgAlO:Eu²⁺, where A comprisesat least one of Ba, Ca or Sr. The preferred aluminate phosphor may havevarious magnesium, aluminum and oxygen molar ratios and is commerciallyavailable under the name “BAM.” For example, one preferred BAM phosphormay be written as AMg₂Al₁₆O₂₇:Eu²⁺, where A preferably comprises atleast 90% Ba ions. This phosphor has the following formula:(Ba_(1-x)Eu_(x))Mg₂Al₁₆O₂₇, where 0<x≦0.2, preferably x=0.07.Alternatively, BAM has the following molar ratios: BaMgAl₁₀O₁₇: Eu²⁺.The BAM phosphor has an emission peak at about 450 nm due to the Eu²⁺activator on the A lattice site. The emission peak shifts from 450 nm toa higher wavelength as the amount of barium ions substituted withstrontium ions increases.

[0063] Other examples of a third phosphor having a peak emissionwavelength between 420 and 480 nm comprise divalent europium activatedaluminate phosphors selected from an EO*AlO:Eu²⁺ phosphor, an EAlO:Eu²⁺phosphor and/or a GAlO:Eu²⁺ phosphor, where E comprises at least one ofBa, Sr or Ca ions and G comprises at least one of K, Li, Na or Rb ions.Preferably, E comprises Ba ions substituted with 0-10% of Sr or Ca ionsand G comprises K substituted with 0-10% of Li, Na or Rb ions.Preferably, the EO*AlO:Eu²⁺ phosphor comprises z(BaO)*6Al₂O₃:Eu²⁺ orz(Ba_(1-x)Eu_(x))O*6Al₂O₃, where 1≦z≦1.8, and 0<x≦0.2. The EAlO:Eu²⁺phosphor preferably comprises BaAl₁₂O₁₉:Eu²⁺ or (Ba_(1-x)Eu_(x))Al₁₂O₁₉where 0<x≦0.2. The GAlO:Eu²⁺ phosphor preferably comprisesKAl₁₁O_(11.07):Eu²⁺ or (K_(1-x)Eu_(x))Al₁₁O_(11.07), where 0<x≦0.2. TheEO*AlO, EAlO and GAlO phosphors are described in the followingreferences, each incorporated herein by reference in their entirety: A.L. N. Stevels and A. D. M. Schrama-de Pauw, Journal of theElectrochemical Society, 123 (1976) 691; J. M. P. J. Verstegen, Journalof the Electrochemical Society, 121 (1974) 1623; and C. R. Ronda and B.M. J. Smets, Journal of the Electrochemical Society, 136 (1989) 570.

[0064] In one aspect of the present invention, the third phosphor maycomprise a blend of SECA, BAM and/or one or more aluminate phosphors inorder to optimize the color or other emission properties, if desired.

[0065] 5. The Optional Fourth Phosphor

[0066] The optional fourth luminescent material may be any phosphor,which in response to the incident radiation 2 from the radiation source1, emits visible light having a peak emission wavelength of about 620 nmto about 670 nm. This red emitting phosphor may be added to the first,second and third phosphors to improve the CRI of the white light emittedby the combination of phosphors. Since the CRI is a measure of how thetest colors appear under illumination from the phosphor compared tounder illumination from a black body, the white light emitted fromphosphor will better approximate the white light from a black body ifthe phosphor emission comprises additional individual colors. If theradiation source 1 comprises an LED having a peak emission wavelengthbetween 360 and 420 nm, then the second phosphor may comprise anycommercially available phosphor having the peak emission wavelengthbetween 620 and 670 nm and a high efficacy and quantum efficiency forincident radiation having a peak wavelength between 360 and 420 nm. Forexample, the Mn⁴⁺ activated fluorogermanate phosphor fits this criteria.

[0067] For example, the fluorogermanate phosphor may comprise amagnesium fluorogermanate phosphor, Mgo*MgF*Geo: Mn⁴⁺, preferably thecommercially available 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺, phosphor. This phosphoremits a structured red luminescence band having six peaks at roomtemperature between 623 and 664 nm.

[0068] 6. The Phosphor Blend

[0069] According to one preferred aspect of the present invention, thefirst, second, third and optionally fourth phosphors are interspersed.Most preferably, the phosphors are blended together to form a uniformblend. The amount of each phosphor in the blend depends on the type ofphosphor and the type of radiation source used. However, the first,second, third and optionally fourth phosphors should be blended suchthat the combination of the emission 9 from the phosphors appears whiteto a human observer 8.

[0070] Alternatively, the first, second, third and optionally fourthphosphors may comprise discrete layers formed over the radiation source1. However, the upper phosphor layers should be substantiallytransparent to the radiation emitted by the lower phosphors.

[0071] The composition of the phosphor powder blend may be optimizedbased on the number of phosphors used, the desired blend CRI andefficacy, the composition of the phosphors and the peak emissionwavelength of the radiation source 1. For example, in order to decreasethe color temperature of the phosphor blend for a constant excitationradiation wavelength, the ratio of blue to orange emitting phosphors maybe decreased. In order to increase the CRI of the phosphor blend, afourth phosphor, such as a red emitting phosphor, may be added to theblend.

[0072] The phosphor blend of a first preferred aspect of the presentinvention preferably contains at least three phosphors, wherein thewhite light emitted by the phosphor blend in response to incident orexcitation radiation having a peak wavelength between 360 and 420 nmcomprises a color temperature between 3000K and 6500K, a CRI above 70and an efficacy of above 200 lm/W. More preferably, the blend efficacyis above 264 lm/W and the color temperature is between 3300K and 4100K.Most preferably the efficacy is above 340 lm/W.

[0073] The preferred first, second and third phosphors of the firstpreferred aspect of the invention comprise strontium pyrophosphate,alkali earth silicate and SECA, respectively. The composition of theblend of the first preferred aspect comprises about 55 to about 75weight percent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor, about 11 to about 22 weightpercent (Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor and about 13 to about 22 weightpercent (Sr,Ba,Ca,Mg)₅(PO₄)₃Cl:Eu²⁺ phosphor.

[0074] The high CRI phosphor blend according to a second preferredaspect of the present invention preferably contains at least fourphosphors, wherein the white light emitted by the phosphor blend inresponse to incident radiation having a peak wavelength between 360 and420 nm comprises a color temperature between 3000K and 4100K, a CRIabove 90 and an efficacy above 200 lm/W. More preferably, the blendefficacy is above 264 lm/W and the color temperature is between 3300Kand 3800K.

[0075] The preferred first, second, third and fourth phosphors of thesecond preferred aspect of the invention comprise strontiumpyrophosphate, alkali earth silicate, SECA, and magnesiumfluorogermanate, respectively. The composition of the blend of thesecond preferred aspect comprises about 11 to about 43 weight percentSr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor, about 9 to about 15 weight percent(Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor, about 6 to about 14 weight percent(Sr,Ba,Ca,Mg)₅(PO₄)₃Cl:Eu²⁺ phosphor, and about 30 to about 71 weightpercent 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ phosphor.

[0076] However, other phosphors having the desired peak emissionwavelengths may be used instead of or in addition to the phosphorsdescribed above. For example, for radiation sources other than LEDs,phosphors that have a high efficacy and high quantum efficiency forincident radiation having a peak wavelength of 254 nm and 147 nm, may beused for fluorescent lamp and plasma display applications, respectively.The mercury gas emission in a fluorescent lamp has a peak emissionwavelength of 254 nm and Xe plasma discharge in a plasma display has apeak emission wavelength of 147 nm.

[0077] 7. The Illumination System

[0078] According to the first preferred embodiment of the presentinvention, the first, second, third and optionally fourth phosphorpowders are placed into a white light illumination system containing anLED radiation source. The white light illumination system may havevarious different structures.

[0079] The first preferred structure is schematically illustrated inFIG. 3. The illumination system includes a light emitting diode chip 11and leads 13 electrically attached to the LED chip. The leads 13 maycomprise thin wires supported by a thicker lead frame(s) 15 or the leadsmay comprise self supported electrodes and the lead frame may beomitted. The leads 13 provide current to the LED chip 11 and thus causethe LED chip 11 to emit radiation.

[0080] The LED chip 11 is encapsulated within a shell 17 which enclosesthe LED chip and an encapsulant material 19. Preferably, the encapsulantcomprises a UV resistant epoxy. The shell 17 may be, for example, glassor plastic. The encapsulant material may be, for example, an epoxy or apolymer material, such as silicone. However, a separate shell 17 may beomitted and the outer surface of the encapsulant material 19 maycomprise the shell 17. The LED chip 11 may be supported, for example, bythe lead frame 15, by the self supporting electrodes, the bottom of theshell 17 or by a pedestal mounted to the shell or to the lead frame.

[0081] The first preferred structure of the illumination system includesa phosphor layer 21 comprising the first, second, third and optionallyfourth phosphors. The phosphor layer 21 may be formed over or directlyon the light emitting surface of the LED chip 11 by coating and drying asuspension containing the first, second, third and optionally fourthphosphor powders over the LED chip 11. After drying, the phosphorpowders form a solid phosphor layer or coating 21. Both the shell 17 andthe encapsulant 19 should be transparent to allow white light 23 to betransmitted through those elements. The phosphor emits white light 23which comprises the orange, blue-green, blue and optionally red lightemitted by the first, second, third and optionally fourth phosphors,respectively.

[0082]FIG. 4 illustrates a second preferred structure of the systemaccording to the first preferred embodiment of the present invention.The structure of FIG. 4 is the same as that of FIG. 3, except that thephosphor powders are interspersed within the encapsulant material 19,instead of being formed over the LED chip 11. The first phosphor powdersmay be interspersed within a single region of the encapsulant material19 or throughout the entire volume of the encapsulant material. Thephosphor powders are interspersed within the encapsulant material, forexample, by adding the powders to a polymer precursor, and then curingthe polymer precursor to solidify the polymer material. Alternatively,the phosphor powders may be mixed in with the epoxy encapsulant. Otherphosphor interspersion methods may also be used. The phosphor powdersmay be premixed prior to adding a mix of these powders to theencapsulant material 19 or the phosphor powders may be added to theencapsulant material 19 separately. Alternatively, a solid phosphorlayer 21 comprising the first, second, third and optionally fourthphosphors may be inserted into the encapsulant material 19 if desired.In this structure, the phosphor layer 21 absorbs the radiation 25emitted by the LED and in response, emits white light 23.

[0083]FIG. 5 illustrates a third preferred structure of the systemaccording to the first preferred embodiment of the present invention.The structure of FIG. 5 is the same as that of FIG. 3, except that thephosphor layer 21 containing the first, second, third and optionallyfourth phosphors is formed on the shell. 17, instead of being formedover the LED chip 11. The phosphor layer 21 is preferably formed on theinside surface of the shell 17, although the phosphor layer 21 may beformed on the outside surface of the shell, if desired. The phosphorlayer 21 may be coated on the entire surface of the shell or only a topportion of the surface of the shell 17.

[0084] Of course, the embodiments of FIGS. 3-5 may be combined and thephosphor may be located in any two or all three locations or in anyother suitable location, such as separately from the shell or integratedinto the LED.

[0085] According to the second preferred embodiment of the presentinvention, the first, second, third and optionally fourth powders areplaced into a white light illumination system containing a fluorescentlamp radiation source. A portion of a fluorescent lamp is schematicallyillustrated in FIG. 6. The lamp 31 contains a phosphor coating 35comprising the first, second, third and optionally fourth phosphors on asurface of the lamp cover 33, preferably the inner surface. Thefluorescent lamp 31 also preferably contains a lamp base 37 and acathode 39. The lamp cover 33 encloses a gas, such as mercury, whichemits UV radiation in response to a voltage applied to the cathode 39.

[0086] According to the third preferred embodiment of the presentinvention, the first, second, third and optionally fourth phosphorpowders are placed into a white light illumination system containing aplasma display device. Any plasma display device, such as an AC or a DCplasma display panel may be used, such as the devices described on pages623-639 of the Phosphor Handbook, Edited by S. Shionoya and W. M. Yen,CRC Press, (1987, 1999), incorporated herein by reference. FIG. 7schematically illustrates one cell of a DC plasma display device 41. Thecell contains a first glass plate 42, a second glass plate 43, at leastone cathode 44, at least one anode 45, a phosphor layer 46 comprisingthe first, second, third and optionally fourth phosphors, barrier ribs47 and a noble gas space 48. In an AC plasma display device, an extradielectric layer is added between the cathode and the gas space 48. Anapplication of a voltage between the anode 45 and the cathode 44 causesthe noble gas in space 48 to emit short wavelength vacuum ultravioletradiation (VUV), which excites the phosphor layer 46 causing it to emitwhite light.

[0087] 8. The Processing Method

[0088] The individual phosphors may be made, for example, by any ceramicpowder method, such as a wet chemical method or a solid state method.

[0089] Preferably, the method of making the first phosphor comprisingeuropium and manganese doped strontium pyrophosphate phosphor comprisesthe following steps. First, the starting compounds of the first phosphormaterial are manually blended or mixed in a crucible or mechanicallyblended or mixed in another suitable container, such as a ball mill, toform a starting powder mixture. The starting compounds may comprise anyoxide, phosphate, hydroxide, oxalate, carbonate and/or nitrate startingphosphor compound. The preferred starting phosphor compounds comprisestrontium hydrogen phosphate, SrHPO₄, manganese carbonate MnCO₃,europium oxide, Eu₂O₃, and ammonium hydrogen phosphate (NH₄)HPO₄powders. The (NH₄)HPO₄ powder is preferably added in an amountcomprising 2% in excess of the stoichiometric ratio per mole of thefirst phosphor produced. A small excess of the Sr compound may also beadded if desired. Calcium, barium and magnesium starting compounds mayalso be added if it is desired to substitute some or all of thestrontium with calcium, barium and/or magnesium. The starting powdermixture is then heated in air at about 300 to 800° C. for about 1-5hours, preferably at 600° C. The resulting powder is then re-blended andsubsequently fired in a reducing atmosphere at about 1000 to 1250° C.,preferably 1000° C., to form a calcined phosphor body or cake.Preferably the starting powder mixture is calcined in a furnace in anatmosphere comprising nitrogen and 0.1 to 10% hydrogen for four to tenhours, preferably eight hours, and subsequently cooled in the sameatmosphere by turning off the furnace.

[0090] Preferably, the method of making the second preferred(Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor comprises the following steps. First, thestarting compounds of the phosphor are manually blended or mixed in acrucible or mechanically blended or mixed in another suitable container,such as a ball mill, to form a starting powder mixture. The startingcompounds may comprise any oxide, hydroxide, oxalate, carbonate and/ornitrate starting phosphor compound. The preferred starting phosphorcompounds comprise barium carbonate BaCO₃, strontium carbonate SrCO₃,calcium carbonate CaCO₃, europium oxide, EU₂O₃, and silicic acid,SiO₂*xH₂O. Preferably, a flux, such as CaF₂ is added to the startingmaterials in an amount of 0.5 to 3 mole percent per mole of the phosphorproduced. The starting powder mixture is then fired a first time in acarbon containing atmosphere, such as in a charcoal containingatmosphere at 1200 to 1400° C. for 5 to 7 hours to form a first calcinedphosphor body or cake. The resultant cake is then ground and milled to apowder. This powder is then annealed or fired a second time in areducing atmosphere at about 900 to 1200° C. to form a second calcinedphosphor body or cake. Preferably the powder is annealed in a furnace inan atmosphere comprising nitrogen and 0.1 to 10% hydrogen for two to sixhours.

[0091] The solid calcined phosphor bodies may be converted to a firstphosphor powder in order to easily coat the phosphor powder on a portionof the white light illumination system. The solid phosphor body may beconverted to the first phosphor powder by any crushing, milling orpulverizing method, such as wet milling, dry milling, jet milling orcrushing. Preferably, the solid body is wet milled in propanol, methanoland/or water, and subsequently dried.

[0092] The third and fourth phosphors are commercially available asphosphor powders and thus, their exact method of manufacture is notsignificant. The synthesis of BAM and SECA phosphors is described onpages 398-399 and 416-419 of S. Shionoya et al., Phosphor Handbook, CRCPress (1987, 1999), incorporated herein by reference. In general, amethod of making a commercial BAM phosphor involves blending startingmaterials comprising barium carbonate, magnesium carbonate, alumina oraluminum hydroxide, europium oxide and optionally a flux, such asaluminum fluoride or barium chloride. The starting powder mixture isthen fired in a reducing atmosphere at about 1200 to 1400° C. to form acalcined phosphor body or cake. The cake may be reground and refiredunder the same conditions. A method of making a commercial SECA phosphorinvolves blending starting materials comprising strontium carbonate,strontium orthophosphate, strontium chloride and europium oxide. Thestarting powder mixture is then fired in a reducing atmosphere at about1000 to 1200° C. to form a calcined phosphor body or cake. The cake isthen ground into a phosphor powder.

[0093] The first, second, third and optionally fourth phosphor powdersare then blended or mixed together to form a phosphor powder blend ormixture. The powders may be manually blended in a crucible ormechanically blended in another suitable container, such as a ball mill.Of course, the phosphor powder blend may contain more than four powders,if desired. Alternatively, the bodies may be pulverized and blendedtogether.

[0094] The phosphor powder blend is then placed into the white lightillumination system. For example, the phosphor powder blend may beplaced over the LED chip, interspersed into the encapsulant material orcoated onto the surface of the shell, as described above with respect tothe first preferred embodiment of the present invention.

[0095] If the phosphor powder blend is coated onto the LED chip or theshell, then preferably, a suspension of the phosphor powder blend and aliquid is used to coat the LED chip or the shell surface. The suspensionmay also optionally contain a binder in a solvent. Preferably, thebinder comprises an organic material, such as nitrocellulose orethylcellulose, in a solvent such as butyl acetate or xylol. The binderenhances the adhesion of the powder particles to each other and to theLED or the shell. However, the binder may be omitted to simplifyprocessing, if desired. After coating, the suspension is dried and maybe heated to evaporate the binder. The phosphor powder blend acts as thephosphor layer 21 after drying the solvent.

[0096] If the phosphor blend is to be interspersed within theencapsulant material 19, then the phosphor blend may be added to apolymer precursor, and then the polymer precursor may be cured tosolidify the polymer material. Alternatively, the phosphor blend may bemixed in with the epoxy encapsulant. Other phosphor interspersionmethods may also be used.

[0097] If the phosphor blend is placed into a fluorescent lamp or aplasma display, then a suspension of the phosphor powder blend and aliquid is used to coat the lamp or plasma display interior surface. Thesuspension may also optionally contain a binder in a solvent, asdescribed above.

9. SPECIFIC EXAMPLES

[0098] The following examples are merely illustrative, and should not beconstrued to be any sort of limitation on the scope of the claimedinvention.

Example 1

[0099] Three blends of three phosphors were prepared by the abovementioned process. The blend composition was varied based on the peakemission wavelength of the radiation source to be used with the blend.In general, for LED radiation sources having a peak emission orexcitation wavelength between 370 and 405 nm, the amount of the firstorange emitting phosphor in the blend increased while the amount of thesecond blue-green and third blue emitting phosphors decreased withincreasing excitation wavelength. The excitation wavelength, the blendcomposition, the CIE color coordinates (ccx and ccy), the colortemperature, the CRI and the efficacy of the blend are summarized inTable II, below. TABLE II PHOSPHOR EXCITA- BLEND Color Efficacy TION λ(WT %) ccx ccy T (K) CRI (lm/W) 380 mm SrP (57.5) .4011 .3807 3507 70.5346.4 BASI (21.5) SECA (21.0) 390 mm SrP (61.4) .3995 .3830 3565 70.7347.3 BASI (19.4) SECA (19.2) 405 mm SrP (73.7) .3899 .3791 3767 72.3349.6 BASI (12.1) SECA (14.2)

[0100] In the above table, the following abbreviations were used:BASI=(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄;SECA=(Sr,Ba,Ca)₅(PO4)₃Cl:Eu²⁺; SrP=Sr₂P₂O₇:Eu²⁺Mn²⁺. Efficacy is definedas the product of the system luminosity times 683 lm/W, where 683 lm/Wis the peak luminosity at 555 nm. System luminosity is defined as (∫F(λ) Y(λ) dλ)/(∫ F(λ) dλ), where F(λ) is the emission spectrum and Y(λ)is the eye sensitivity curve. As illustrated in Table II, the colortemperature of the blends varied from 3507 to 3767 K, the CRI variedfrom 70.5 to 72.3 and the efficacy varied from 346.4 to 349.6 lm/W.These high efficacy blends are preferred for the white lightillumination systems sold in the North American lighting market.

Example 2

[0101] Three blends of four phosphors were prepared by the abovementioned process. The blend composition was varied based on the peakemission wavelength of the radiation source to be used with the blend.In general, for LED radiation sources having a peak emission orexcitation wavelength between 370 and 405 nm, the amount of the first,second and third phosphors in the blend increased while the amount ofthe fourth phosphor decreased, with increasing excitation wavelength.The excitation wavelength, the blend composition, the CIE colorcoordinates (ccx and ccy), the color temperature, the CRI and theefficacy of the blend are summarized in Table III, below. TABLE IIIPHOSPHOR EXCITA- BLEND Color Efficacy TION λ (WT %) ccx ccy T (K) CRI(lm/W) 380 mm SrP (12.7) .4017 .3835 3519 93 285 BASI (10.0) SECA (7.4)MgF (69.9) 390 mm SrP (17.6) .4065 .3793 3374 93.5 272.2 BASI (11.8)SECA (9.0) MgF (61.6) 405 mm SrP (41.5) .3967 .3743 3557 91.3 264.7 BASI(14.2) SECA (12.8) MgF (31.5)

[0102] In the above table, the following abbreviations were used:BASI=(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄;SECA=(Sr,Ba,Ca)₅(PO4)₃Cl:Eu²⁺; SrP=Sr₂P₂O₇:EU²⁺Mn²⁺ andMgF=3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺. As illustrated in Table III, the colortemperature of the blends varied from 3374 to 3557 K, the 10 CRI variedfrom 91.3 to 93.5 and the efficacy varied from 264.7 to 285 lm/W. FromTable III, it is apparent that the addition of the fourth red emittingphosphor results in a significant CRI increase. These high CRI blendsare preferred for the white light illumination systems sold in theEuropean lighting market.

[0103] The preferred embodiments have been set forth herein for thepurpose of illustration. However, this description should not be deemedto be a limitation on the scope of the invention. Accordingly, variousmodifications, adaptations, and alternatives may occur to one skilled inthe art without departing from the spirit and scope of the claimedinventive concept.

What is claimed is:
 1. A white light illumination system comprising: alight emitting diode; a first luminescent material having a peakemission wavelength of about 575 to about 620 nm; and a secondluminescent material having a peak emission wavelength of about 495 toabout 550 nm, which is different from the first luminescent material;and a third luminescent material having a peak emission wavelength ofabout 420 to about 480 nm, which is different from the first and secondluminescent materials.
 2. The system of claim 1, wherein the white lightemitted by the system lacks any significant visible component emitted bythe light emitting diode.
 3. The system of claim 1, wherein the lightemitting diode peak emission wavelength is 360 to 420 nm.
 4. The systemof claim 3, wherein the light emitting diode comprises an InGaN activelayer having a peak emission wavelength is between 370 and 405 nm. 5.The system of claim 1, wherein the radiation emitted by the lightemitting diode does not significantly penetrate through the first,second and third luminescent materials.
 6. The system of claim 1,further comprising a fourth luminescent material having a peak emissionwavelength of about 620 nm to about 670 nm.
 7. The system of claim 1,wherein the first luminescent material comprises a first APO:Eu²⁺, Mn²⁺phosphor, where A comprises at least one of Sr, Ca, Ba or Mg.
 8. Thesystem of claim 7, wherein: the first phosphor comprises(A_(1-x-y)Eu_(x)Mn_(y))₂ P₂ O₇; where A comprises Sr; 0<x≦0.2; and0<y≦0.2.
 9. The system of claim 7, wherein the second luminescentmaterial comprises a second phosphor selected from at least one of: a)an ASiO:Eu²⁺ phosphor, where A comprises at least one of Ba, Ca, Sr orMg; b) an ADSiO:Eu²⁺ phosphor, where A comprises at least one of Ba, Caor Sr and D comprises at least one of Mg or Zn; or c) an AAlO:Eu²⁺phosphor, where A comprises at least one of Ba, Sr or Ca.
 10. The systemof claim 9, wherein: the ASiO:Eu²⁺ phosphor comprises an(A_(1-x)Eu_(x))₂SiO₄ phosphor, where A comprises Ba, Sr and Ca and0<x≦0.2; the ADSiO:Eu²⁺ phosphor comprises an (A_(1-x)Eu_(x))₂ DSi₂O₇phosphor, where 0<x≦0.2; or the AAlO:Eu²⁺ phosphor comprises an(A_(1-x)Eu_(x)) Al₂O₄ phosphor, where 0<x≦0.2.
 11. The system of claim9, wherein the third luminescent material comprises a third phosphorselected from at least one of: d) an AMgAlO:Eu²⁺ phosphor where Acomprises at least one of Ba, Ca or Sr; e) a DPOCl:Eu²⁺ phosphor where Dcomprises at least one of Sr, Ba, Ca or Mg; f) an EO*AlO:Eu²⁺ phosphor,where E comprises at least one of Ba, Sr or Ca; g) an EAlO:Eu²⁺phosphor, where E comprises at least one of Ba, Sr or Ca; or h)GAlO:Eu²⁺ phosphor, where G comprises at least one of K, Li, Na or Rb.12. The system of claim 11, wherein: the AMgAlO:Eu²⁺ phosphor comprises(A_(1-x)Eu_(x))Mg₂Al₁₆O₂₇, where A comprises Ba and 0<x ≦0.2; theDPOCl:Eu²⁺ phosphor comprises (Sr_(1-y-z) Ba_(y) Ca_(z))_(5-x)Eu_(x)(PO₄)₃Cl, where 0.01≦x≦0.2, 0≦y≦0.1 and 0≦z≦0.1; the EO*AlO:Eu²⁺phosphor comprises z(Ba_(1-x)Eu_(x))O*6Al₂O₃, where 1≦z≦1.8and 0<x≦0.2;the EAlO:Eu²⁺ phosphor comprises (Ba_(1-x)Eu_(x))Al₁₂O₁₉, where 0<x≦0.2;or the GAlO:Eu²⁺ phosphor comprises (K_(1-x)Eu_(x))Al₁₁O_(11.07), where0<x≦0.2.
 13. The system of claim 11, wherein: the first phosphor, thesecond and the third phosphor are interspersed in a phosphor blend; thelight emitting diode peak emission wavelength is about 360 to about 420nm; and the white light emitted by the phosphor blend in response toincident light emitting diode radiation comprises a color temperaturebetween 3000K and 6500K, a CRI above 70 and an efficacy above 300 lm/W.14. The system of claim 13, wherein the phosphor blend comprises: about55 to about 75 weight percent Sr₂P₂O₇: Eu²⁺, Mn²⁺ phosphor; about 11 toabout 22 weight percent (Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor; and about 13 toabout 22 weight percent (Sr,Ba,Ca,Mg)₅(PO₄)₃Cl:Eu²⁺ phosphor.
 15. Thesystem of claim 14, wherein: the radiation source comprises an LEDhaving a peak emission wavelength of about 380 nm; and the phosphorblend comprises: about 57.5 weight percent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor;about 21.5 weight percent (Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄phosphor; and about 21 weight percent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor.16. The system of claim 14, wherein: the radiation source comprises anLED having a peak emission wavelength of about 390 nm; and the phosphorblend comprises: about 61.4 weight percent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor;about 19.4 weight percent (Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄phosphor; and about 19.2 weight percent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺phosphor.
 17. The system of claim 14, wherein: the radiation sourcecomprises an LED having a peak emission wavelength of about 405 nm; andthe phosphor blend comprises: about 73.7 weight percent Sr₂P₂O₇: Eu²⁺,Mn²⁺ phosphor; about 12.1 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; and about 14.2weight percent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor.
 18. The system ofclaim 11, further comprising a fourth phosphor comprising3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺.
 19. The system of claim 18, wherein: the firstphosphor, the second, the third phosphor and the fourth phosphor areinterspersed in a phosphor blend; the light emitting diode peak emissionwavelength is about 360 to about 420 nm; and the white light emitted bythe phosphor blend in response to incident light emitting dioderadiation comprises a color temperature between 3000K and 4100K, a CRIabove 90 and an efficacy of above 200 lm/W.
 20. The system of claim 19,wherein the phosphor blend comprises: about 11 to about 43 weightpercent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 9 to about 15 weight percent(Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor; about 6 to about 14 weight percent(Sr,Ba,Ca,Mg)₅(PO₄)₃Cl:Eu²⁺ phosphor; and about 30 to about 71 weightpercent 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ phosphor.
 21. The system of claim 20,wherein: the radiation source comprises an LED having a peak emissionwavelength of about 380 nm; and the phosphor blend comprises: about 12.7weight percent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 10 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; about 7.4 weightpercent (Sr,Ba,Ca)₅(PO₄)₃Cl:EU²⁺ phosphor; and about 69.9 Weight percent3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺.
 22. The system of claim 20, wherein: theradiation source comprises an LED having a peak emission wavelength ofabout 390 nm; and the phosphor blend comprises: about 17.6 weightpercent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 11.8 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; about 9 weightpercent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor; and about 61.6 weight percent3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺.
 23. The system of claim 20, wherein: theradiation source comprises an LED having a peak emission wavelength ofabout 405 nm; and the phosphor blend comprises: about 41.5 weightpercent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 14.2 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; about 12.8 weightpercent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor; and about 31.5 weight percent3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺.
 24. The system of claim 13, furthercomprising: a shell containing a light emitting diode; an encapsulatingmaterial between the shell and the light emitting diode; and wherein: a)the phosphor blend is coated over a surface of the light emitting diode;b) the phosphor blend is interspersed in the encapsulating material; orc) the phosphor blend is coated onto the shell.
 25. A white lightemitting phosphor blend comprising at least three phosphors, wherein thewhite light emitted by the phosphor blend in response to incidentradiation having a peak wavelength between 360 and 420 nm comprises acolor temperature between 3000K and 6500K, a CRI above 70 and anefficacy above 200 lm/W.
 26. The phosphor blend of claim 25, wherein theefficacy is above 264 lm/W and the color temperature is between 3300Kand 4100K for incident radiation having a peak wavelength between 370and 405 nm.
 27. The phosphor blend of claim 26, wherein the efficacy isabove 340 lm/W.
 28. The of claim 27, wherein the phosphor blendcomprises: about 55 to about 75 weight percent Sr₂P₂O₇:Eu²⁺, Mn²⁺phosphor; about 11 to about 22 weight percent (Ba,Sr,Ca)₂SiO₄:Eu²⁺phosphor; and about 13 to about 22 weight percent(Sr,Ba,Ca,Mg)₅(PO₄)₃Cl:Eu²⁺ phosphor.
 29. The phosphor blend of claim28, wherein the phosphor blend comprises: about 57.5 weight percentSr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 21.5 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.5))₂SiO₄ phosphor; and about 21 weightpercent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor.
 30. The phosphor blend ofclaim 28, wherein the phosphor blend comprises: about 61.4 weightpercent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 19.4 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; and about 19.2weight percent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor.
 31. The phosphor blendof claim 28, wherein the phosphor blend comprises: about 73.7 weightpercent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 12.1 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; and about 14.2weight percent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor.
 32. The phosphor blendof claim 26, wherein the CRI is above
 90. 33. The phosphor blend ofclaim 32, further comprising a fourth phosphor comprising3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺.
 34. The phosphor blend of claim 32, whereinthe phosphor blend comprises: about 11 to about 43 weight percentSr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 9 to about 15 weight percent(Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor; about 6 to about 14 weight percent(Sr,Ba,Ca,Mg)₅(PO₄)₃Cl:Eu²⁺ phosphor; and about 30 to about 71 weightpercent 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ phosphor.
 35. The phosphor blend ofclaim 34, wherein the phosphor blend comprises: about 12.7 weightpercent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 10 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; about 7.4 weightpercent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor; and about 69.9 weight percent3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ phosphor.
 36. The phosphor blend of claim 34,wherein the phosphor blend comprises: about 17.6 weight percentSr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 11.8 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; about 9 weightpercent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor; and about 61.6 weight percent3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ phosphor.
 37. The phosphor blend of claim 34,wherein the phosphor blend comprises: about 41.5 weight percentSr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor; about 14.2 weight percent(Ba_(0.65),Sr_(0.2),Ca_(0.1)Eu_(0.05))₂SiO₄ phosphor; about 12.8 weightpercent (Sr,Ba,Ca)₅(PO₄)₃Cl:Eu²⁺ phosphor; and about 31.5 weight percent3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ phosphor.
 38. A white light illuminationsystem, comprising: a radiation source; a first APO:Eu²⁺,Mn²⁺ phosphor,where A comprises at least one of Sr, Ca, Ba or Mg; a second phosphorselected from at least one of: a) an ASiO:Eu²⁺ phosphor, where Acomprises at least one of Ba, Ca, Sr or Mg; b) an ADSiO:Eu²⁺ phosphor,where A comprises at least one of Ba, Ca or Sr and D comprises at leastone of Mg or Zn; or c) an AAlO:Eu²⁺ phosphor, where A comprises at leastone of Ba, Sr or Ca; and a third phosphor selected from at least one of:d) an AMgAlO:Eu²⁺ phosphor where A comprises at least one of Ba, Ca orSr; or e) a DPOCl:Eu²⁺ phosphor where D comprises at least one of Sr,Ba, Ca or Mg; f) an EO*AlO:Eu²⁺ phosphor, where E comprises at least oneof Ba, Sr or Ca; g) an EAlO:Eu²⁺ phosphor, where E comprises at leastone of Ba, Sr or Ca; or h) GAlO:Eu²⁺ phosphor, where G comprises atleast one of K, Li, Na or Rb.
 39. The system of claim 38, wherein: thefirst phosphor comprises (A_(1-x-y)Eu_(x)Mn_(y))₂ P₂ O₇, where Acomprises Sr, 0<x≦0.2 and 0<y≦0.2; the ASiO:Eu²⁺ phosphor comprises an(A_(1-x)Eu_(x))₂SiO₄ phosphor, where A comprises Ba, Sr and Ca and0<x≦0.2; the ADSiO:Eu²⁺ phosphor comprises an (A_(1-x)Eu_(x))₂ DSi₂O₇phosphor, where 0<x≦0.2; the AAlO:Eu²⁺ phosphor comprises an(A_(1-x)Eu_(x)) Al₂O₄ phosphor, where 0<x≦0.2; the AMgAlO:Eu²⁺ phosphorcomprises (A_(1-x)Eu_(x))Mg₂Al₁₆O₂₇, where A comprises Ba and 0<x≦0.2;the DPOCl:Eu²⁺ phosphor comprises (Sr_(1-y-z) Ba_(y) Ca_(z))_(5-x)Eu_(x)(PO₄)₃Cl, where 0.01≦x≦0.2, 0≦y≦0.1 and 0≦z≦0.1; the EO*AlO:Eu²⁺phosphor comprises z(Ba_(1-x)Eu_(x))O*6Al₂O₃, where 1≦z≦1.8, and0<x≦0.2; the EAlO:Eu²⁺ phosphor comprises (Ba_(1-x)Eu_(x))Al₁₂O₁₉, where0<x≦0.2; or the GAlO:Eu²⁺ phosphor comprises(K_(1-x)Eu_(x))Al₁₁O_(11.07), where 0<x≦0.2; and further comprising afourth 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ phosphor.
 40. The system of claim 39,wherein: the illumination system comprises an LED lamp, a fluorescentlamp or a plasma display; and the radiation source comprises an LED chipor a gas contained in the fluorescent lamp or a plasma display;
 41. Amethod of making a white light illumination system, comprising: blendinga first phosphor powder having a peak emission wavelength of about 575to about 620 nm, a second phosphor powder having a peak emissionwavelength of about 495 to about 550 nm, and a third phosphor powderhaving a peak emission wavelength of about 420 to about 480 nm to form aphosphor powder mixture; and placing the phosphor powder mixture intothe white light illumination system adjacent a light emitting diode. 42.The method of claim 41, further comprising selecting an amount of thefirst, second and third phosphor powders such that the white lightemitted by the phosphor powder mixture in response to incident radiationhaving a peak wavelength between 360 and 420 nm comprises a colortemperature between 3000K and 6500K, a CRI above 70 and an efficacy ofabove 200 lm/W.
 43. The method of claim 42, wherein the step ofselecting comprises: selecting about 55 to about 75 weight percentSr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor powder; selecting about 11 to about 22weight percent (Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor powder; and selecting about13 to about 22 weight percent (Sr,Ba,Ca,Mg)₅(PO₄)₃Cl:Eu²⁺ phosphorpowder in order to achieve an efficacy above 346 lm/W.
 44. The method ofclaim, 42, wherein the step of selecting comprises: selecting about 11to about 43 weight percent Sr₂P₂O₇:Eu²⁺, Mn²⁺ phosphor powder; selectingabout 9 to about 15 weight percent (Ba,Sr,Ca)₂SiO₄:Eu²⁺ phosphor powder;selecting about 6 to about 14 weight percent (Sr,Ba,Ca,Mg)₅(PO₄)₃Cl:Eu²⁺phosphor powder; and selecting about 30 to about 71 weight percent3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺ phosphor powder in order to achieve a CRI above90.
 45. The method of claim 42, further comprising: placing the lightemitting diode having a peak emission wavelength between 370 and 405 nminto a shell; filling the shell with an encapsulating material; and a)coating a suspension of the phosphor powder mixture and a solvent over asurface of the light emitting diode and drying the suspension; b)interspersing the phosphor powder mixture in the encapsulating material;or c) coating a suspension of phosphor powder mixture and a solvent ontothe shell and drying the suspension.